/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
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 *
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 *
 */

package java.security;

import java.io.IOException;
import java.io.EOFException;
import java.io.InputStream;
import java.io.FilterInputStream;
import java.io.PrintStream;
import java.io.ByteArrayInputStream;

/**
 * A transparent stream that updates the associated message digest using
 * the bits going through the stream.
 *
 * <p>To complete the message digest computation, call one of the
 * {@code digest} methods on the associated message
 * digest after your calls to one of this digest input stream's
 * {@link #read() read} methods.
 *
 * <p>It is possible to turn this stream on or off (see
 * {@link #on(boolean) on}). When it is on, a call to one of the
 * {@code read} methods
 * results in an update on the message digest.  But when it is off,
 * the message digest is not updated. The default is for the stream
 * to be on.
 *
 * <p>Note that digest objects can compute only one digest (see
 * {@link MessageDigest}),
 * so that in order to compute intermediate digests, a caller should
 * retain a handle onto the digest object, and clone it for each
 * digest to be computed, leaving the orginal digest untouched.
 *
 * @author Benjamin Renaud
 * @see MessageDigest
 * @see DigestOutputStream
 */

public class DigestInputStream extends FilterInputStream {

    /* NOTE: This should be made a generic UpdaterInputStream */

  /* Are we on or off? */
  private boolean on = true;

  /**
   * The message digest associated with this stream.
   */
  protected MessageDigest digest;

  /**
   * Creates a digest input stream, using the specified input stream
   * and message digest.
   *
   * @param stream the input stream.
   * @param digest the message digest to associate with this stream.
   */
  public DigestInputStream(InputStream stream, MessageDigest digest) {
    super(stream);
    setMessageDigest(digest);
  }

  /**
   * Returns the message digest associated with this stream.
   *
   * @return the message digest associated with this stream.
   * @see #setMessageDigest(java.security.MessageDigest)
   */
  public MessageDigest getMessageDigest() {
    return digest;
  }

  /**
   * Associates the specified message digest with this stream.
   *
   * @param digest the message digest to be associated with this stream.
   * @see #getMessageDigest()
   */
  public void setMessageDigest(MessageDigest digest) {
    this.digest = digest;
  }

  /**
   * Reads a byte, and updates the message digest (if the digest
   * function is on).  That is, this method reads a byte from the
   * input stream, blocking until the byte is actually read. If the
   * digest function is on (see {@link #on(boolean) on}), this method
   * will then call {@code update} on the message digest associated
   * with this stream, passing it the byte read.
   *
   * @return the byte read.
   * @throws IOException if an I/O error occurs.
   * @see MessageDigest#update(byte)
   */
  public int read() throws IOException {
    int ch = in.read();
    if (on && ch != -1) {
      digest.update((byte) ch);
    }
    return ch;
  }

  /**
   * Reads into a byte array, and updates the message digest (if the
   * digest function is on).  That is, this method reads up to
   * {@code len} bytes from the input stream into the array
   * {@code b}, starting at offset {@code off}. This method
   * blocks until the data is actually
   * read. If the digest function is on (see
   * {@link #on(boolean) on}), this method will then call {@code update}
   * on the message digest associated with this stream, passing it
   * the data.
   *
   * @param b the array into which the data is read.
   * @param off the starting offset into {@code b} of where the data should be placed.
   * @param len the maximum number of bytes to be read from the input stream into b, starting at
   * offset {@code off}.
   * @return the actual number of bytes read. This is less than {@code len} if the end of the stream
   * is reached prior to reading {@code len} bytes. -1 is returned if no bytes were read because the
   * end of the stream had already been reached when the call was made.
   * @throws IOException if an I/O error occurs.
   * @see MessageDigest#update(byte[], int, int)
   */
  public int read(byte[] b, int off, int len) throws IOException {
    int result = in.read(b, off, len);
    if (on && result != -1) {
      digest.update(b, off, result);
    }
    return result;
  }

  /**
   * Turns the digest function on or off. The default is on.  When
   * it is on, a call to one of the {@code read} methods results in an
   * update on the message digest.  But when it is off, the message
   * digest is not updated.
   *
   * @param on true to turn the digest function on, false to turn it off.
   */
  public void on(boolean on) {
    this.on = on;
  }

  /**
   * Prints a string representation of this digest input stream and
   * its associated message digest object.
   */
  public String toString() {
    return "[Digest Input Stream] " + digest.toString();
  }
}
